158 



BIOLOGY OF THE PROTOZOA 



Hypotrichida. They are placed more or less definitely on the 

 ventral surface, a group, variable in number, at the anterior end 

 being known as the frontal cirri, a similar group, also variable in 

 number, near the posterior end being known as the anal cirri, while 

 other groups may form caudal cirri, ventral cirri, marginal cirri, etc. 

 (Fig. 88). 



Vj> 





P.C. 



Fig. 86 



Fig. 87. 



Fm. 86. — Structure of typical Vorticella showing the adoral membranes, AM' 

 I 1/ ,• vestibule, 1*.; contractile vacuole, C.V.; food vacuole, FA'., and posterior 

 circlet of cilia. (After Noland and Finley, from Trans. Am. Microscopical Sue, 

 1931.) 



Fig. 87. — Lembadion conchoides F.'F. (After Faure-Fremiet.) . 



( 'irri are always broader at the base and taper gracefully to a 

 fine point. In cross-section near the base they are either circular, 

 ellipsoidal, quadrilateral or irregular, and always have a basal plate 

 made up of the basal granules of the fused cilia. Under unfavorable 

 conditions of the medium in which the organisms live, and usually 

 after imperfect fixation, the constituent cilia become separated par- 



